A simple method is introduced to measure the refractive index (RI) of a liquid with an experimental device composed of a graduated cylinder and a beaker which are coaxial. A magnified image of the graduated cylinder is formed as the liquid is poured into the beaker. Optical path analysis indicates that the RI of the liquid is equal to the product of the image’s diameter magnification and the RI of air, irrelevant to the beaker. Theoretically, the RI measurement range is unlimited and the liquid dosage could be small as well. The device is used to carry out experiments by means of both the photographic method and telescope method to measure RIs of three kinds of liquids. The results show that the measured RIs all fit their published values well.

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